Microcavity plasma devices have several distinct advantages over conventional discharges. The small physical dimensions of microcavity plasma devices allows them to operate at pressures much higher than those accessible to conventional, macroscopic discharges. When the diameter of a cylindrical microcavity plasma device is, for example, on the order of 200-300 μm or less, the device will operate at pressures as high as atmospheric pressure and beyond. In contrast, standard fluorescent lamps, for example, operate at pressures typically less than 1% of atmospheric pressure. Microcavity plasma devices may be operated with different discharge media (gases or vapors or a mixture thereof) to offer output in the visible and nonvisible (ultraviolet, vacuum ultraviolet, and infrared, for example) wavelength ranges. Microcavity plasma devices are able to produce light more efficiently than other conventional discharge systems and do so on the microscopic scale.
Microcavity plasma devices developed over the past decade have been demonstrated to be well-suited for a wide variety of applications. An exemplary application for a microcavity plasma device array is to a display. Since the diameter of single cylindrical microcavity plasma devices, for example, is typically less than 400-500 μm, devices or groups of devices offer a spatial resolution that is desirable for a pixel in a display. In addition, the efficiency of a microcavity plasma device exceeds that of a conventional plasma display panel, such as those used in high definition televisions.
Early microcavity plasma devices exhibited short lifetimes because of sputtering that damaged metal electrodes used in the early, DC-driven devices. Polycrystalline silicon and tungsten electrodes extend lifetime but are higher cost materials and difficult to fabricate with present techniques.
Research by the present inventors and colleagues at the University of Illinois has pioneered and advanced the state of microdischarge devices. This development has led to practical devices including one or more important features and structures. For example, microcavity plasma devices can be operated continuously at gas pressures beyond one atmosphere at power loadings exceeding 100 kW/cm3. The ability to interface plasma in the gas or vapor phase with an e-h+ plasma in semiconductor devices has been demonstrated. MEMs and semiconductor processes have been applied to the fabrication of devices and arrays.
This research by present inventors and colleagues at the University of Illinois has resulted in exemplary practical devices. For example, semiconductor fabrication processes have produced exemplary densely-packed arrays of uniform microcavity plasma devices. An example array fabricated in silicon has demonstrated 250,000 discharge devices in a 25 cm2 active area. It has been demonstrated that the arrays can be used to excite phosphors in a manner analogous to plasma display panels, but at luminous efficacy levels that are not achievable with conventional plasma display panels. Another important device is a microcavity plasma photodetector that exhibits high sensitivity. Phase locking of microcavity plasma devices has also been demonstrated. Devices have been fabricated in ceramic material systems.
The following U.S. patents and patent applications describe microcavity plasma devices resulting from these research efforts. Published Applications: 20050148270—Microdischarge devices and arrays; 20040160162—Microdischarge devices and arrays; 20040100194—Microdischarge photodetectors; 20030132693—Microdischarge devices and arrays having tapered microcavities; U.S. Pat. No. 6,867,548—Microdischarge devices and arrays; U.S. Pat. No. 6,828,730—Microdischarge photodetectors; U.S. Pat. No. 6,815,891—Method and apparatus for exciting a microdischarge; U.S. Pat. No. 6,695,664—Microdischarge devices and arrays; U.S. Pat. No. 6,563,257—Multilayer ceramic microdischarge device; U.S. Pat. No. 6,541,915—High pressure arc lamp assisted start up device and method; U.S. Pat. No. 6,194,833—Microdischarge lamp and array; U.S. Pat. No. 6,139,384—Microdischarge lamp formation process; and U.S. Pat. No. 6,016,027—Microdischarge lamp.
U.S. Pat. No. 6,541,915 discloses arrays of microcavity plasma devices in which the individual devices are fabricated in an assembly that is machined from materials including ceramics. Metallic electrodes are exposed to the plasma medium which is generated within a microcavity and between the electrodes. U.S. Pat. No. 6,194,833 also discloses arrays of microcavity plasma devices, including arrays for which the substrate is ceramic and a silicon or metal film is formed on it. Electrodes formed at the tops and bottoms of cavities, as well as the silicon, ceramic or glass microcavities themselves, contact the plasma medium. U.S. Published Patent Application 2003/0230983 discloses microcavity plasma devices produced in low temperature ceramic structures. The stacked ceramic layers are arranged and micromachined so as to form cavities and intervening conductor layers excite the plasma medium. U.S. Published Patent Application 2002/0036461 discloses hollow cathode plasma devices in which electrodes contact the plasma/discharge medium.
Additional exemplary microcavity plasma devices are disclosed in U.S. Published Patent Application 2005/0269953, entitled “Phase Locked Microdischarge Array and AC, RF, or Pulse Excited Microdischarge”; U.S. Published Patent Application No. 2006/0038490, entitled “Microplasma Devices Excited by Interdigitated Electrodes;” U.S. patent application Ser. No. 10/958,174, filed on Oct. 4, 2004, entitled “Microdischarge Devices with Encapsulated Electrodes,”; U.S. patent application Ser. No. 10/958,175, filed on Oct. 4, 2004, entitled “Metal/Dielectric Multilayer Microdischarge Devices and Arrays”; and U.S. patent application Ser. No. 11/042,228, entitled “AC-Excited Microcavity Discharge Device and Method.”